reprinted with permission from Journal Of Pesticide Reform/ Spring 1994 • Vol.14, No.1

Northwest Coalition For Alternatives To Pesticides/NCAP P.O. Box 1393, Eugene, Oregon 97440 / (5 41)344 -504438

Alternatives:

LEAST TOXIC APHID MANAGEMENT

By BECKY LONG

 

Every spring, aphids are one of the first pests to arrive in the yard and garden. Rarely noticed when numbers of aphids are small, larger aphid colonies can damage plants.

 

However, it is important to realize that most plants can tolerate modest aphid infestations and that aphids are always present at some level in all garden environments. A combination of physical and biological controls can help keep the aphid population in your yard  and garden at tolerable levels.

 

Life Cycle and Biology

There are over 4,000 species of aphids.

Appearance varies, but all aphids are small (1/8 inch long) insects with soft bodies and mouths adapted for sucking the nutrient-rich juice out of plant tissue. Most feed on only one kind of plant or a few closely related species, but around 10 percent feed on a variety of different plants. So aphids spotted on your rose bush will not necessarily spread and move to your cabbage patch.1

 

Many aphid species have a remarkable life cycle that enables them to reproduce rapidly. In the fall, female aphids lay eggs in the protected cracks and crevices of plants and trees. In the spring just as plants are sprouting new growth, the overwintered eggs hatch. Incredibly, all the hatching aphids are females that without mating give live birth to daughters who in turn are born ready to give live birth to more daughters. This reproductive process continues throughout the growing season. For some greenhouse species, no male aphids have ever been identified! But most outdoor species complete the life cycle at the end of the growing season by producing males and egg bearing females that mate and lay eggs to over-winter.1,2

 

Monitoring and Detection

Aphid populations vary year to year and plant to plant so regular inspection is an important step in determining if you have an escalating aphid problem. Check for aphids on the undersides of leaves and on new growth. Moderate aphid populations usually don’t cause noticeable damage.

 

Aphids feed by sucking the sweet syrupy sap from plants. Some aphids can spread plant diseases. Yellowing, leaf curl, puckering, leaf galls, distortion of new growth and weakened plants may all be signs of a large aphid infestation. Honeydew, black mold and ants are also indicators of a significant aphid infestation. Ingesting more sap than they can absorb,

aphids excrete the excess in the form of honeydew.

 

Harmless but messy, honeydew forms a sticky coating on leaves and fruit and an unattractive black, sooty mold may develop. Honeydew from tree feeding aphids may fall on sidewalks and cars creating a sticky nuisance. Ants are attracted to honeydew and sometimes protect and care for aphid colonies in order to maintain the honeydew supply.3

Biological Controls and Natural Enemies

Aphids have many natural enemies including lady beetles, green and brown lacewings (also known as “aphid lions”), spiders, various flies, mini-wasps, and aphid midges. In most garden environments, these natural enemies keep the aphid population under control. Lady beetles, in both the adult and larval stages, eat around 50 aphids a day.4  However, beneficial insects don’t appear until there is an adequate food supply, in other words plenty of aphids and other tasty prey. So there may be times, especially in the spring when beneficial populations are too small to keep aphid populations from increasing. Beneficial insects can be attracted to gardens by planting a variety of flowering plants. Parsley, carrots, fennel, caraway, coriander, daisies, sunflowers, yarrow, artemisia, marigolds, zinnias, and asters are all especially attractive to beneficial insects.4 A few aphid infested weeds can also serve as an attractive, interim food supply for beneficial insects in the early spring. Finally beneficial insects can be purchased and released into garden environments, but released predators are mobile and do not necessarily stay in your garden.1

 

Physical Controls

Natural biological control of aphids is achievable, but low to moderate aphid populations must be tolerated especially early in the season when numbers of beneficial insects lag behind aphid populations. While waiting for beneficial insects to become abundant, there are a number of physical controls that will reduce aphid populations.

 

• Plant wisely: Avoid aphid problems by not choosing plant varieties that attract aphids such as birch or spruce trees. If you must have aphid attractive plants or trees, place them where aphid presence and honeydew production won’t become an unbearable nuisance.4,5

 

• Maintain plant health: Healthy plants are most resistant to pest problems. Stressed or unhealthy plants act as magnets to pest populations.5

 

• Water washing: Aphids can be washed off plants with a strong stream of water. Repeat every three to four days until beneficial insects control aphid populations. Washing early in the day so the plant can dry off before evening reduces the risk of fungal disease.1

 

• Wipe, clip or prune: Use cloth gloves to wipe small aphid colonies off leaves or buds. Infested parts of plants can be pinched off or pruned. Dispose of these clippings in hot compost or in soapy water.1,6

 

• Control nitrogen levels: Aphids reproduce more rapidly on plants with high nitrogen levels. Instead of highly soluble nitrogen fertilizers, use composted or urea-based fertilizers that release moderate levels of nitrogen over time.1,6

 

• Use row covers: For garden beds, finely woven row cover materials are available at garden centers. These covers are an effective barrier to insects, but light, air, and water easily penetrate for good plant growth.6

 

• Control ants: To maintain continuing supplies of aphid honeydew, an ant delicacy, certain ant species protect aphids by killing their natural enemies. Apply sticky barriers, available at garden stores, to the stems or trunks of plants to prevent ant access.1,6

 

• Insecticidal soap: If a regular water wash doesn’t work, adding soap or detergent can help dislodge aphids. The fatty acids in soaps can also serve as an insecticide, killing aphids on contact. (Test your soap on a small part of the plant before washing the entire plant.)

 

Summary

Chemical pesticides are often ineffective in aphid management because they temporarily reduce aphid populations while decimating beneficial insect populations. However, a combination of physical and biological controls can effectively keep the aphid population in your yard and garden at tolerable levels.

References

1. Olkowski, W., S. Daar, and H. Olkowski. 1991. Common-sense pest control: Least-toxic solutions for your home, garden, pets and community. Newtown, CT: Taunton Press.
2. Borror, D., D. DeLong, and C. Triplehorn. 1976. An introduction to the study of insects. New York, NY: Holt, Rinehart and Winston.
3. Gilkeson, L. 1992. Aphids: Safe and sensible pest control. Victoria, BC Ministry of Environment, Land and Parks. Pesticide Management Branch. (June.)
4. Thurston County Local Hazardous Waste Program.

Aphids: A guide to aphid control for the earth-friendly gardener. A pamphlet in Thurston County’s “Common Sense Gardening” series.

5. Johnson, D., 1990. Aphids: Safe and successful control. Seattle, WA: Washington Toxics Coalition.
6. Daar, S. and H. Olkowski. 1992. Least-toxic ways to control aphids. Common Sense Pest Control 8(2):14-1

APHIDS ON HOUSEPLANTS

The aphids on your houseplants are probably the same species found in your yard and garden. The most common indoor aphid and the most difficult to control is the green peach aphid which comes in several colors: pale green, yellow, and pink. Indoor aphids have an extremely high reproductive rate since the male fertilization and egg laying parts of the life cycle are unnecessary. Methods for controlling aphids indoors are similar to those used outdoors.1

 

• Inspect new plants for pests before bringing them home.
• Quarantine new plants and aphid infested plants for several weeks in a separate room. Treat aphid infested plants during this isolation period.
• Screen windows to prevent aphid en-try from outside.
• Prune and pinch off plant pieces with aphids.

• In warm weather, take aphid infested plants outdoors and wash with a strong stream of water.
• Spot treat plants with spray of soapy water. (Test your soap on a small section of the plant first.)
• Use a slow release fertilizer to maintain slow but steady plant growth. Divide recommended fertilization doses into smaller more frequent doses. For example, break a monthly amount into quarters and fertilize weekly.
• For true devotees of beneficial insects, indoor releases are an effective means of controlling indoor aphids. Lady beetles, lacewings and aphid-eating gall midges are good candidates for indoor control.
• Researchers have found that commercial brands of vegetable cooking oil (coconut, corn, peanut, safflower, soybean, and sunflower) mixed with common liquid dishwashing detergent makes an effective and economical solution that kills aphids and other common insect pests. Mix one tablespoon dishwashing detergent to one cup oil to make the basic stock. Add 1 to 2 1/2 teaspoons of this concentrate to one cup water, then spray on plants. This solution may injure some plants so test a small part of the plant first.2

1. Olkowski, W., S. Daar, and H. Olkowski. 1991. Common-sense pest control: Least-toxic solutions for your home, garden, pets and community. Newtown, CT: Taunton Press.
2. Grossman, J., 1990. Horticultural oils: New summer uses on ornamental plant pests. The IPM Practitioner 8(8):1-10